Harmandir Sahib, Punjab's Golden Temple (so named because it is literally plated in gold) may be Sikhism's holiest house of worship, but it, like any other gurdwara, is open to men and women of any faith. In fact, a Muslim was invited to lay the first foundation stone.
Service is a major tenet of Sikhism. Everyday, hundreds of volunteers at the gurdwara feed tens of thousands of people for free.
Visitors must wear a headcovering, remove shoes, & wash their feet before entering.